What does the term efficiency mean?
- A$\text{efficiency} = \frac{\text{useful energy input}}{\text{total energy output}}$
- B$\text{efficiency} = \frac{\text{total energy input}}{\text{total energy output}}$
- C$\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}}$
- D$\text{efficiency} = \frac{\text{total energy output}}{\text{total energy input}}$